Automatic telephone system



Sept. 29, 192s. 1,554,999

J. E. GARDNER AUTOMATIC TELEPHONE sxfs'rlm Filed Oct. 27, 1922 4 Sheets-Sheet 1 1 l r I 999 1 -h-CfG-- UU:

l r9 9S S 4% N N l@ @L u gg l \Q%\\ Imran m:-

\ Uhu E Eard'ner sept-29,1925. 1 1,554,999

' J. E. GARDNER AUTOMATIC TELEPHONE SYSTEI( med oct. 2v. 1922 '4 sheets-shui 2 -Inuen u Uhn Eardner sepf. 29, 192s.

J. E. GARDNER AUTOMATIC TELEPHONE sYs'rnll Sept. 29, 1925. 1,554,999A

J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM E uhu E Eard-ner Zwe/H@ Patented Sept. 29, 1925.

ff unrif-ED PATENT o Joni; E'GARDNER, or ciiIoAGo, ILLINoIs, Asszrenon me, Anworten@ mEcrnicrcoM-i HDW,` OFCHICAGO, ILLINOIS, A-ooRPoRATIoN oFILLiNoIs. *i

t AUmoMATic y'minnenom: y.svsmlnn Application mea ocmhei 27, i922.` serial no. 557,268.'

To. all whom t may concern." y

Be, it known that I, JfoHN E. GARDNER, a citizen of Canada, and a resident ofv Chi` cago in' the county of Cook and State of Illinois,1 have invented certain new and useful Improvements in Automatic Telephone Systems, of which the fell-owing is a specification;y e

The present invention rela-tes in general to automatic telephonel systems, but is more particularly concerned with small Vsystems. which are commonly known as privateautomatic exchangesv Exchanges of this naturel l are usually installed byprivate concerns, and.

owing to the, more exacting requirements of the subscribers in exchanges of this. type, it isoften necessary to provide features which are unnecessary in a publicexchange.` The .y present invention is Concerned with alfea 20 ture of this character which isy commonly known as conference calling.. ,Thisis an arrangement lto enable an olicial of a Colnf pany, having'a private automaticv exchange,

,1 totali: toy a number of` his employes simultaneously; in other words,l a number oftelephonellines may be connected together for conference purposes.` "llitherto, in an` ar-y rangement ofthis character, it was possible i to establish a lconference Connection. without maintaining a series of switches for each line includedfin the conference.V However, in such. system, it was necessary to prefix at least two digits to the 'callednuinberfo I eachsu'bs'criber included in the conference connection( The present invention contemplates a scheme. of this nature, wherein thetrunk lines. and switches usedduring the conference are reduced to. a ininimuni, and at the sanne timefmaking it. unnecessary" todial more than the ordinary `directory number4 ofthe subscribers desired, with vone exception-,..` this exception being in tliefcase` of the subscriberfrstcalled when it is 'necessary to prefix two. digits.4

The, particular manner inwhich this other results are accomplished will be exsl plained fully hereinafter, reference being had to the accompanying drawings. Referring now to thedrawings, Figs. `1 2, and'` 3. show byI nieanso-f' the `usual circuit diagrams sufficient ofthe apparatusinftheprivate automatic exczlhangeV to` enable the invention to be readily explained and understoodlf Eig.` 4 shows arplnodication of the line switches have accesstotrunk lines lead-'f im ing to connector switchesI one of whichs.` shown at H',"`Fig. 2. i l 'r v The `connector H isl of therwellknoiivn Strowger vertical 4and rotarytype, and hasv the usual set of lQObank 'contacts arranged in ten rows or levels., In all casesthe. connector and othenlo'cal `switches function as ordinary connectors, except in :oneinl stance, which exceptionison the conference numben On the conference number,r the local connectors function 'tol switch through; in the saine manner as a selectorfswitch'.

The conference number, as shown in "the drawings,` has associatedmwith 1it the bank contacts 1344136, i inclusive, accessible to the` connector The trunkl'ihe extending lrorn this set of bank contactsterrninat'es inthe special connector H,.l l`ig;` 3. e The con? tacts 13S-140,inclusive, are the contacts` as` sociated with the line of the substation A accessible to 'the `connector The bank contact i set coinpris'ing bank contacts '142- 144, inclusive, arefthelterininals 4of the line ofthe substation' A in theconnector The conference connectorjH Fig.,` 3, is used only for conference purposesaridihas access to lines of'all thesubScrbers whoV are entitled toiconierence service." lThe bank contacts in the connector] "ll," inlwhichl the local" subscribers linesjfterminate, l are `ioinecl to the inultiplelbetween the local con-fl nectors, but before being `-so oined, t one line conductor of"v each subscjriberA 'fis passed. dimagrire winding-pf a any, umsehen@ repre-sentedin the `dg.@swingsaan einem.,

whicharethe rela-ys-individualv4 tofth" lines leading fof ne essere@ briefly described', a detailed explanation of its operationjwillfinow be "givenjjgi 'For this' purpose, it will be' assumed that the-subl` scriber at substation A desires to hold a con'- ference.v Under these conditions,this subscriberwill remove his receiver and callthe regular local number of the first subscriber desired in the conference, prelixing'the digj its of the conference number 30, Vhen the receiver is removed at substation A, a'ci'r` cuit is closed for the line relay 13 of the line switch C over the line conductors 11" aiid12 in series. Upon operating, Vrelay 13 atA its armature closesa circuit' which includes the switching relay '14 and the steppingmagnet 15in series, and atits arma -i tfure2`1 connects the test wiper 26 to the above lcircuit ata point midway between the l switching relay 'and thesaid'stepping magf, whether the trunk line withwhich the wip! net.' The operation now depends upon ers lof the line switch C are 'associated is or is v,not busy.

,Iv-f the trunk line isv busy, the't'est contact withfwhich the: testviper 26 is in engagenient will be grounded, and as a result the Switching relay 14 will beshortl ciicuited and the stepping magnet 15, being supplied'with direct ground by way ofthe said test wiper, willoperate as a buzzer to advance the switch wipers *stepl by step'V in 'searchfof' an l, idlel trunkl line.y

y l It will beassumed, how ever, thatV whenthe call :is 'iiiitiated,the wipersf of ythe liiie'switch ,C are standing upilgtlie bank contacts shown in the drawings,

., audit will beifurtlierassu'med that the ltrunk line 'extending from these contacts is idle.

` Under these circumstances, the test vContact .29` willA have no ground potential on it and, when the receiver is removed, the eiiergiza-` tion of the line Arelay 13 is `followed imme-` j diately by the energization of the switching relay 14. It may be stated at this point that the switching relay is of very high resist-k ance. so as to prevent the operation ofthe stepping magnet'` l5 at this time. As a result 'of the energization of the switching` l relay 13 the lineJ` conductors 11 and 12 are disconnected from the line relay 13 and from ground,frespectively, andare extended by i, way of'armatures 16 and 18 and theirffront contacts, wipers 25 and 27, bank contacts 28 an'dO, trunkgconductor's 3S and 46 arma tures 7,5 and`78 andtlieirback c'ontacts,`to

the upperand lower win'ding'sffofjlinerelay` l 50 of the local connectoInH.'`

pares the operating circuits of the connector Hat its armature 66, and at armaturey 67 establishes a holding circuit which extends from ground byway of front contact and armature 67, release trunk conductor 39, bank Contact 29, wiper. 26,*a`rmature 17 'and its front contact, 'and' through the winding of the switching relay 14 and the stepping magnetyl to battery..v The above circuit is com pleted before ,the slow acting` line relay 13 has had time to deenergize and serves to maintain 'the' switching relay 14 energized throughout the connection. Ground is also extendedfby way ofthe private normal conductor 31 to multiply connected test` con tacts in the banks of the connector switches,

whereby the said line is protected' from i'n-V trusion in the ordinary manner.

The calling subscribernow operates his calling' device in accordance with the first digit'of the conference number, which isl the digit 3.Y Three interruptions are lthereby produced inthe line circuit of relay "50, which deenergizes a corresponding number of times, each time completing a'circuit eX? springs'are shifted and the circuit for thel vertical magnet. is completed over' a new path which is the "same as the one'previously traced except that it includes the off normal springs69' and 77, and armature 70and`its front fcontact, yslow actingy relayy 52 being now energized. i' yBythe operation ofthe vertical magnet 100,'the switch wipers 120-122, inclusive, are raisedvstep by step until they are lplaced opposite the third level of bank contacts. Thev slow actingv series relay 52` which is energized'in series with the vertical magnet, lmaintains its armature attracted throughout 'the vertical ,movement` of the switch and at thetend vof tliefvertical move-y ment deenergizes, transferring theoperating circuit to the rotary magnet v102. Y

The calling subscriber now operates his calling device in accordance. with the Second digit of the conference number, name1y,-the digit O. lTen interruptions'are thereby pro? duced' in ythecircuit of the linel relayy 50,' wliichoperates in ,response thereto and at each retraction of its armature completes aV circuit extending as followsz'ground by way of armature 65and its backv contact, armature 66 and its front contact, off normal spi'i'ngs'69 and 77, 'armature 70 and its back contact, back contact yand armature ,86, armature p99*y and its back., contact, and.V thence through the winding of thea-of tary magnet- V102 to battery. Magnet 102 operates to rotatethe'wipers 12,0-122, inclusive, into engagement with the` y tenth vset of contacts inthe"third level which', it'will lli inclusive., The. Slow act-ing relay 5.8 is, energized in multiple. with the `rotary magnet.,

aule-l operates to. connect the test Wiper 121 -to thetest. relay Springs' 83 land Secre cem. springe adapted to be .shifted into.- engegement by the com on the switch shaft when the switch wipers are brought. into' engage-ment with :the con-ferencev number 3.0,. Zhen the springs 8.3 and 84 are `brougl-it int-o. engagement, a circuit is. completed extending from ground on release trunk conf doctor by way of; armature 9.7 and its` back contact, through springs 84V and 83, andy through upper winding of relay 5.6 to bat.-y

teryf. Rel-ey- 5,6 operates to establish ci lockf ing circuit for itself et its armature 81 and armatures SQ and S2 prepares a `point in the dialling circuit of thev auxiliary" conT nec-tor H. If the line, is busy, the operation of?l the springs 83 and 84 will' have no. func-1 tion at this time exceptus above stated.

Assuming the conference number toybe busy, ground will. be present on the. test contact 135., engaged by the test wiper 121. A circuit Will thereby be completed extending from the said grounded test Contact bv Way oft test wiper 121, normallyV closed springs `controlled byrelay 59, armature 9.0 and its front Contact, und thence through the Winding of' the test relay 5.7 to. battery. Upon operating, the Irelay 5f? prepares u locking' circuit for itself at armature 85, opens the rotary magnet circuit by the operati-on of armature 86, and at armature 817' pinces` the busy.y tone. upon. the lower line conductor of the calling subscriber, thereby notifying hliin `thatl for the present vthe conference number is; inaccessible. The calling subscriber will.,` therefore, replace his receiverfuponl the switchhoolr, thereby relezis ling: Vthe switches C` und H in u nim-inerto, be. explained; hereinafter.

However, it Willbe assumed'in the present cese thm; `the conference number is .idle when connection thereto is attempted by the connector EL Under these circumstances,4 no ground will be. present upon the test conV tiret eng-gedy by test wiper. 12E and testJ relay 5,7 will not be energized. A circuit tlwncoinpleted upon che deenergization. the. sloiv Acting rele-y 58; extending from ground upon release trunk conductor 3.9,. eirmoturen.- endif-.s beck Contact, through bliellppr :Winding of the` switching relay' 5.9,y back contact. and miniature 90, normal-'ly closed springs controlled by armature 98, test wiper 121 test 4con-tact; 135, endgthrough the resistance E' to; battery.I Relay 59 euergilzes over thisy circuit and, upon operating, establishes. a locking circuit; for `itself et @ceinture 9'?, and. at armatures 95 and 100; prefieres other points. in tlie=dialli1ng--ci`rcuit extending; tothe connector switch H", Fig.. 3;; .Afurtherresult of. the energization, of

relay 5.9 is that at armature.. 97 .the` Short. circuit. is removed yfrom relay 55. circuit is. then effective, elfrtendin-gg` from` ground' on the` release `trunk conductor 3.9i,

tlirougfh the winding of relay sprlngs, Se ali-(118:3, andl ithroughtbe ulglpier4v winding of relay 5.6 tosbettery.- Relay 55,1

upon energizing, completes .the .dialling cire cuit to .the euxiliory connector Het: "the seine time disconnectingthe line relay: lll-usfdielhngcircuit moludesgthe line relay` 3.611 of the connector H which is. energized over e circuitl extending' from. ground.- thuough the lower Windingof relay' 3.02., conductor 1.57, benk Contact. 13,6., wiper 122,.. freut contact endermature 100, erflnetureni. :uid its` front contact, front Contact and; :Miniature: 78,-conductor 40, benk: contact 3.0,

wiper 27.',-front Contact and ernieturel',

line conduct-or l2, switchhook springs, re.-

ceiver, tru nslnitter, end calling" device ofl the f substation A, lune conductor 1l, arinature lfwmid its front: con-tec@ wiperZ, benk Contact 28, conductor 38, eigrueti'ire' and its fromy cont-ect, through. the Winding of the low? resistance relay 5.3-, erlnature 9.5 and. its front contact, Wiper 152,0,Y benk con tact 13d, conductor ,15.6, and through the Lrpfp'e-irwinding of liuc relay 31011. of the con Hector to. battery.. Relays 5.3 and.30-1. over tl1is;ci1cuit,. Relay et. its: armature le maintains the; circuit; of che, Slow acting release releyloftbie., locsilY conneetorH closed so. rcley'- does` not retract its urm'ature even though the.. lille. relay 50 is deenergizech. thereby. preventing the releaseof the switcliH and?. mentainilng the line switch .C in en operetcd ion.; Relay.-V 301, upon encrguing, coninlctesthe circuit: of the slow' ectngrreleesereloy 3.02. of the.l zu'rkli'ery conference connector The latter relay pre-peres the` switch. circle-ts foroperetion in. the usuel reanner.,` f

'libe-calling subscri vet substation. rsfllnev.` now cell' ther-wo digits-ofthe desired local; Subscriber-S number.. Whentheca ing de vice is: operated' fory the first digit ofthe 11:1ui1-- belg-a. ser-ies; of interruptions is produced the circuit of' the line `relrxz 361.1 of the'conhector H, and. elsointbecircuit ofthe low. 111; cescries: relzry- 53 rin.- thei conn@ or The relay 53. 1..'esp-onclsby-vi-bretn miniature, butV es; the ifeleyf 5l is slowaet g, che connector f andthe; line Switch. C ere maintained; opcrfecl by the cout-inueclener gizction. of reley 51;1-- Intheconneciior Hf.. relay 301 opera-tes in responsefto, thefinterruptions produced its circuits; euclsends acorresponding Ysessiesof' impulses: `tri/che. vertical inegue't- 3.0.9.;y Thefrstl: ofi these im. pulses traverses@ circuit extending from ground4 by wey of? armature 323,31@ itsbneki contact, aumzrtuce. 32 andzits front. contra-et, off normal ysprings- 326 ellid 32T, through' if whidingf ofthcsloyv acti-ngreluy 303;,andA

so? y lili() lili through the winding4 of the vertical magnet 309 to` battery. Upon the first vertical step of the switch shaft, the off normal springs are shifted :and vthe remaining impulses to the vert-ical magnet are sent over a different 3504352, inclusive, step by step until thev said wipers are brought opposite to the level of bank cont-acts in which is located the con- `tact sct associated with the desired suibscribers line. The slow acting relay 303 is energized in series with the vertical magnet 309, maintains its armature attracted throughout the vertical movement of the switch, and atthe termination thereof decnergizes and 'transfers the operating-circuit torthe. rotary magnet 311. Whenthe off normal springs are operated upon the first vertical movement of the switch shaft, a. circuit is completed extending from ground by way of front contact and armature 324, working contact of off normal spring 329 and the said spring, and through the winding of relay 300 to battery. Upon operating, relay 300 at armatures 320 and 321 disconnects the conference trunk comprising conductors 379 and 369 rfrom connection with the conductors 156 and 157. The reason for this operation will appear fully subsequently.

.sNVhen the calling device at substation A' is operated for the next and nal digit of the desired partys number, the line circuit of relay 301 is opened a plurality of times. At-each deenergization, relay 301 sends an impulse of current over the following circuit: ground by way of armature 323 and its back contact, armature 325 andits front contact, off normal springs 326 and 328, armature 332 and its backV contact, back contact and armature 338, armature 346 and its back contact, 'and through the winding of magnet 311 to battery. Magnet 311 operates to rotate the switch wipers 350-'-352, inclusive, into engagement with the bank contact set associated withthe line of the desiredy subscriber at substation A,'which, as shown in the drawings, are the bank contacts- 358- 360, inclusive. The slow acting relay 306 is energized in multiple with the rotary magnet and operates to connect the ftest wiper 351 to the test relay 305.- 1 f y f Assuming that the desiredv'lineis lousyv at the; present time', there will be a ground potential'uponthetest contact 359 and the test relay 305 ywill be energized. Upon operating, relay 305 .closes a point in its locking circuit, :which circuit is'completed upon the deenergization vof slow acting relay 306, at armature 336 closes a point inthe circuit of the release magnet, at armature 335, opens a a leadfrom ythe busy signalling machine to conductor 157. `'Upon the deenergization of slow acting relay 306, a circuit is completedy extending from ground by way of front contact and armature-324, armature 331 and its back contact, armature 340 and its back con tact, fro-nt Contact and armature 336, worlc ing Contact of off normal spring 330 andthe said spring, andtlirough the winding of the release magnet 310'to battery. Magnet 310 operates to restore the connectorH to normaly position, its own circuit being opened at the off. normal springs when the switch shaft returns to normal. By the opening'of the off normal springs, vthe relay 300 also deenergizes and reconnects the conference trunk with `conductors 156 and 157. As a `lead from thev busy signalling machineI is con` nected to conductor 157, the calling subscriber is given an audible signal in order to inform him that the` desired line is busy. There are two courses now open` tol the sub.- scriber at substation A. He may'either re.- place his receiver and attempt to establish the conference at alater timewhen the line of the substation A becomes idle, or, if he desires, he may call the remaining 'subfscribers desired in-the conference succes sively. f y If the` subscriber at substation A replaces his receiver, the connection .will be released in a manner which will be described hereinafter.,l f.

yIt will be assumed,however, that theline ofthe substation A is idle when the wipers of the connector H are brought into engagement with the bank contacts '358-4360, inclusive. Under these-conditions, there will be no ground potentiai upon the test contact 359 and the test relay305 will not be energized. Then, following the deenergization ofthe slow acting relay 306, a circuit is completed whichmay bey tracedfrom ground by way of frontl contact and yarmature 324, working-contact.o-foff normal 'spring' 329 andthe said` spring, armature`333 .and .its backY contact, `back Contact and f armature 335, through the upper winding of the switching relay 307, back Contact and ar.- mature 341, normally .closedfspringscontrolled by armature 344, test wiper351, test contact 359', private normal conductor-154, conductor 35, through/ theI winding ofthe switching relay 32, and throu'ghthe-winding of the rotary vmagnet 33 to battery. Relays 32 and 307 are energizedover thiscircuit. Upon operating,` relay 132 only partially vaty tracts itsLarmatures, enough. tovdisconnect the linenof the substation A from .-.its nor-l malbattery land ground connections in the line switch'Cl This partial operation is .cuit of l ,to the fact that its winding is shunted by due to a mechanical interflocking device which is controlled by the armature of the line relay 3l which isvnow normal.

Inthe connector H, relay 307, upon energizing, at armature 345 closes a locking circuit for itself, at armature 34:4 places direct ground upon the test contact 359, at armature B46 opens the rotary magnet circuit, and at armaturesll `and 34:7 completes the ringing circuit. Signalling current from the generator Gen is now intermittently projected out on the called line until any answer is obtained. It will be noted that the relay 372 is in the line cirthe substation A. However, due

a condenser and also because it is constructed so as not to respond to ringing current,.i`t lis not actuated at the present time.

lVhen the called subscriber responds, a circuit is completed for the ring-cutoff' relay 301ir in the connector H in series with the individual relay 372. Relay 372, upon operating, at armature 376 places ground upon theprivatenormal conductor 154 in order to maintain the line of the substation A busy, and at arma-tures 377 and 378 connects the line ofthe substation A with the conference trunk comprising conductors 37 9 and 369. y y y Relay 304 at armature 334 closes a locking circuit for itself and at armaturev 333 completesa circuit for the release magnet 310,. at the same time opening the llocking and energizing' circuit for the switchingrelay 307.` Relay 30,7 immediately deenergizes todisconnect thepsignalling current and to restore certain other circuits to nor mal. Magnet 310 operates to release the switch in the usual manner. When the off normal springs are operated at the time the switch shaft reaches normal, the locking circuit of the ring-cut-ofll relay 304 isv opened and alsotlie circuit relay 300. The circuit of the release magnet is also opened at the roti' normal springs. Byv the release of the connector H the original energizing circuit of the relay 379.1is opened. However, this relay ismaintained energized over theline circuit of the substation'A, battery being supplied from thewindings of the conference trunk relay 370. The subscriber at substation A may now converse with the subscriber at substation A, the talking circuit extending over' the heavyr conductors in the drawing and over the conference trunk. The su'bscriberat substation A will inform the called party that a conference is to be held and for him to hold the line.

The Vcalling subscriber will now operate his calling device in accordance with the two digits of; the nextpartys number. By these operations the connector H is again operated in the same manner as before until its wipers are brought into engagement with the bank contacts of the wanted subscriberls line. The relay 300 is, of course, energized upon the first vertical step of the switch shaft, and operates to disconnect the conf A. Vhenthe connection is made with Athe i line ofthe desired'party, the relay 307.is

energized, assuming that the line is l id-le,

ringing current is applied to the called line. Then the `called subscriber answer-s, the

ri1'ig-cut-olf relay 304: inthe connector is energized as is the'relay in series with the called line. The relay `in series kwithth'e called line operates to associate that line withA the conferencetrunk in the 1same n'rjanner ashas already been described. `The `relay 304 in the connector H brings about the release of this switch in the same `manner as before. The calling subscriber at substation A can now converse with this lpartyfove'r the conference trunk and inform him that a conference is being held.

In the above inan-nervall the parties desired may be included in. the conference, and no switches will be held up except the connection from the `substation A to the conference number. It will be rememberedthat when the `connection was `lirst extended lto the line ofthe substation A that it `was assumed that this line was busy, and it 4was pointed out at kthat time that the subscriber at substation A, if he so desired, could im` mediately call the remainingparties in the conference. This operation will now. briefly described. v"the connector switch H is now in normal position, it will be operatedl in `the same manner as has been previously described res onsive to the two digits of the called `su scribers number.

When the slow acting relay SOSiS-energized in series with the vertical `magnet SQQ, the locking circuit of the test relay i 305 is opened, and this relay deenergizes to `remove the busy tone from conductorl? and to restore certain `other.circuitsto normal.

The remaining operations of, the connector H take. place inf a manner already., described. .Y

It will now` be assumed that duringnthe -v establishmentof theconference connection, the last `line desired by the calling partyvis busy. Under these conditions, the connector H willbe released anda busy tone4 willy be applied to conductor 157... The subscriber at substation A may still 4desire to confer i with the parties' already called even though order to remove the busy tone, the subscriber at substatiolrA will call a special number providedfor thatpurpose.l -Vyhen this number is called,` the connector HHre- Ahe cannot obtainy the party last called.. In Y spends in'theusual manner and raises its wipers' and then rotates them into engagement with the contact set associated with this number, which it will .be assumedy are the 4bank contacts 390-392, inclusive. Vhe'n 'engagement is made with this set of bankl contacts, relay 307 is energized and also vthe relay304, as the resistance R is bridged across the bank contacts 390 'and 392. Relay 304 energizes to bring' about. the release ot the connector H in the ordinary manner. By the above operation, the busy tone is removed from the conductor 157 and the connector H` is lett so that if it develops during the conference that another subscriber is desired, that subscriber may be called by dialling'his directory number in the usual manner.

lVhen thefconference is terminatechthe subscribers called' will vreplace' ytheir receivers as vwill the subscriber at substation A. The replacement of the receiver at substation A brings about the deenergization 'of the line relay 301 of the 'connector H and "also the relay 53 of, the connector H. Relay 301, upon deenergizing, opens the circuit of the slow acting relay 302. The latter relay, 'upon retracting its armatures, brings about the relea'seof the connector H.l The deenergization ofv relay 53 `in the connector H opens the circuit of the slow acting relay 51 which also deenergizes. Upon retracting its' armatures, relay 51 opens the circuit ot certainl relays in the connector H, and also closes the circuit of the release magnet 101. In this manner, the' connector H restored to normal., the removal ot ground from release trunk conductor 39by the relay 51 'deenergizing, Athe holding 'circuit of the switching relay 14 in lthe line switch C is openedv'and this relay'deenergizes to restore the line-switclr'circuits to normal.v Each subscriber associated with the conference trunk vb'y'replacing, his receiver upon the switclrhoolr,` severs his connection with the conference trunk, the lrelay suchas '372 being deenergized assoon as its associated Avsubscriberreplaceshis receivers. In the above: manner the connection is released. The operation of the invention when the 'connector' H is used having been described, the operation ofthe moditication shown in Fig.' 4 will now bebrietly explained. For `th 1's purpose,'it will beassumed that inthe koriglnal connection when the subscriber at `substation"Ais call'echthat the connector H2 is' 4the one connected lto. Immediately upon 'the' connection being extended to the connector H21, the linelrelay 2 01 'thereof is energizedr andclosesa circuit' ,for the slow 'act1ngfrelay`202- The latter relay operates toprepare the operating 'circuits of the switch in 'the' usual manner.A

ln response to the next operation of the calling'device at substationA, aseries'of in'- terruptions is produced in the line relay circuit, anda'corresponding series of impulses is sent to the vertical magnet 209. Magnet 209 operates to raise the switch Wipers 250-252, inclusive, step by step until these wipers are placed opposite the level of bank contacts in which is located a Contact set associated with the line of the substation A. The slow acting relay 203 is energized in 'se-ries with magnet 209 and operates its armature 231 to close the circu'it'of relay 200, and its armature 232 to preserve vthe vertical magnet, circuit when the offV normal springs are shifted upon the first vertical movement of the switch. At the termination of the vertical operation, the slow acting relay 203 deenergizes and transfers the impulsing 'circuit t the'rotary magnet 211 at armature i 232,'and opens the circuit ofthe relay 200 at armature 231. The operation of relay v200 serves to disconnect the conference trunk lcomprising conductors 279 and 269 from the energized in multiple with therotary m'agmn net.` ARelay 205 operatesto close the circuit of relay 200 at. armature 236, and at armature 253 operates to open a 'point in the talking circuit. The Voperation of armature 235 is without particular function at the' present 4time because the slow acting relay 207 islalso energized. Relay 207, upon operating, at armature242 opens a point 1n the circuit of the upper', winding of relay`204, connects the test wiper 251 to the test relay 2.06 at armature 243, and at armature 244 short circuits the contactsprings comprising armature 240 and itsv back Contact, on the test relay 2 06,.in order yto provide against the opening of the :rotary magnet circuit should the test relay y206 become `energized'by the switclr'wipers being rotated over 'bankl contact sets` associatefd with busy telephone lines. A further result of the cnergiz'ation ot' relay 207, isv that at armature 254 the connection of the lower wiper 252 with theconductor of the switch is opened. p

Assuming rst thatthe line "of the substation A' is idle, there will be'no ground po;-

tential upon the test contact r2.59 andthe `test relay 20G will not be energized.- Then, upon the deenergization ot the slow actingrelay 20T, a circuit is completed extending'fr'om ground by wayof front contact -andlarma- 'ture 224'. working contactT oit" oft normal spring 229 and the said spring, armature 233 `and its back-contact, back Contact and armature 238, throughthe rupper Winding of relay 208, 'back contact and armature 243, nornially yclosedsprings controlled by armature 246, test wiper 25:1, test contact 25 private normal conductors 154 and 35, through the winding of switching relay 32 of line switch C', and through the `Winding of motor magnet 38 to battery. Relays 208 and 32 are energized. Relay 32 operates as ibel'ore to disconnect the normal battery and ground connections from the called lines.

In the connector H2, rela-y 208, upon ener gizing,at'a.r1`nature 2217 establishes a locking circuit for itself,"places directgroiuid upon thetest contact'259 at armature 246, opens the rotary magnet circuit at armature 248, and at armatures 245 and 249 completes the signalling'circuit. Ringing current is now intermittent-ly projected out on the called line until ananswer is obtained.Y Relay 272, which is included in series with the conducw tor 155, is not energized for the saine reason as was stated in the previous explanation in connection IWith relay 272.

Then theicalled` subscriber responds, relays 2T2'and 204 are energized. Relay 272 operates to associate the called subscribers line. withV the conference trunk and also places ground lupon the private normal conductor. Relay 204, upon operating, closes a locking circuit for itself at armature 234, at armature opens the circuit of relay 208, and att-he front contact of this armature completesthe circuit ot' the release magnet 210.. Thedeenergization of relay` 208 brings aboutlthe disconnection of ringing current andthe restoration of certain circuits to normal inthe connector H2. When the switch shaft returns to normal, the release magnet 210 as Well as the relay 204 is deenergized. J'he calling andrcalled subscribers may now converse, the talking circuit being similar to the one already traced in the previous des cription of the connector H'. The subsequent operations of establishing a conference connection will proceed in substantially the saine manner as has been before described.

Then the conference is linally termi# nated, the release of d the connection is brought about by each subscriber replacing" his receiverupon his associated switchhook. `By the replacement of the receiver at substation VA, the release of the switches C, and `H2`cccur in the usual manner. Each subscriberincluded in the conference in replacing -his i receiver disconnects his line fromthe conference trunk` @In thelestablishment of the above conference connection, if the Wipers of the connector H2 are rotated into engagement with a bank contact set associated with a busy `line, the test relay-206 will be energized inthe ordinary manner. Relay 20G, upon operating, preparesa point in its locking been connected with bythe conference connector. The lcalling subscriber at substation A will new converse with the `parties and inform the one he desires -thatsJ `eonference -is being held, and ask the busy subscriber to terminate his presentconnection as soon as possible. To 'terminate this connection, both busy subscribers will replace their' i receivers, thereby removing the guarding potential from the test contact associated with the testvviper` 251. As the test relayi206 is maintained locked by this guardingpotential, it Will nour` deenergize. The energization of relay 206 closes the circuit of the; switching relayv 208. The subsequent operations 'wherein the called subscriber is signalled' and themanner in which he is connected to the conference trunk all take placeas before described.`

It may happen that ivhen'a`b1lsy line is f connected to by the conference connector H2, that the conversation is so rimportant that it is undesirable to abruptly terminate ita] Upon the calling subscriber at substation Abeing informed of this fact, he will operate his calling device for the digit l( By this operation the line relay 201 deenergizes momentarily and sends an impulse of current to the slow acting relay 205. Upon operating, relay 205 at armature 236 closes a circuit forthe relay 200, and atarmatum 235 prepares a circuit for relay 204. Upon energizing, relay 200, in laddition to disconnecting the conference trunk, completes a vcircuit: for relay 204. Relay 204,"upon energizing, brings about the release of the connector H2,--in the lsame manner as if the desired yparty had answered.` By this release, the test relay 206 is deenergized and thel lead from the tone machine T disconnected. y

Having described the manner inwhich conference connections are established, vit will now beA briefly "explained how thesubscriber at substation A may connect with thesubscriber at substation'A2 in an ordinary connection. In. this case, in response to the two digits of the desired subscribers number, the connector H will be operated insubstantially the same manner as before described, though, instead of the Wipers 120H-122, linclusive. being opera-ted into engagement with the contacts 134-136, in-

'free elusive, they will be operated into engagement with .bank contacts l38-140, inclusive. .Another difference is that as the cani springs S3 and S4 are not in yengagement with `each other, neither the relay or 56 will beoperated. `The relay 59 -is energized `.in series.withtheswitching relay 32 in the line switch C in the Yusual manner. -Relay 32, of course, operates to disconnect the called line from its normal battery. `and ground connections. Upon operating', relay 5.9 closes af'locking circuit tor itselfy at armature- 97, places direct ground .upon test contact 139 at armature 98, and at'armatures 95 and 100 closes the signalling circuit. Ringing current from the generator Gen. 1s now connected to the called line. lVhen ythe called subscriber answers, the ring-cut-oftrelay 56'is" energizedv and 'operates at armature .81 to establish a locking circuit for itself, to open the ringing circuit at armatures:` and 82 and' at the front contacts 4ofthese armatures to' complete the talking circuit. Talking current isjsupplied .to the calling'subscriber from 'the windings of the line relay 50, and to y in Y the usual manner.

.7 :Should the line of the substation A have V loeenflnisy when -called' .as above described,

the calling s-i-ibsc'riber islgi'ven rabusy tone .in amanner similar to thatvbetore described.

'f The features 'ot'the invention, having been desfnubedy and ascertained, fwhatlis consid- Aeredtovbe vnew and desired to have pro- "-tected by. Letters Patent will be pointedk out ,in the appended claims.

lVhat vI claim is; y

l. In atelephonesystem, Vtelephone lines, two directively controlled automatic switches operated Asuccessively from a calling one of said telephone lines for establishing' a connection witha called one of said lines, a holding trunk, and means controlled by the responseotthe.subscriber on said called line for connecting such .line to said holding trunk and for releasing. thellast operated switch. ,jf .i f ,w

2. In a telephone system, telephone lines, an automatic switch, a holding ltrunkassociated. with said automatic switch, meanscontrolledfrom a calling one ofsaid lines for extending a connection tor said'switch, means for lthen operating said switch to connect ,with va called .one ot said telephone lines, a source Aof signalling` current, means 'tor automatically applying said source to said .line and means controlled by the response of the subscriber on the said-called line t'or disconnecting said .signal-ling current and for establishing. altalking connection with said calling line independent of said switch but includingv said holding trunk.

3. In a telephone system, an automatic switch, telephone lines, a holding trunk associated lwith said switch, means controlled by a subscriber on a calling one of said lines ttor operating said automatic switch to signal a station on a called one of said lines, and means responsive to the removal of the receiver at said called station for establishing a talking connection with said calling line independent of said switch butincluding said holding trunk.

4. In a telephone system, telephone lines, an automatic switch controlled from a calling one of said lines for extending a connection to a called one of said lines, means for making said called line busy, means in said switch responsive to such busy condition tor releasing only said switch and. for applying a tone to said calling line, and mea-ns wherebyV said calling subscriber may reoperate said switch to! connect with another ot' said lines while maintaining the receiver at the calling substation oit' the'switch hook.

5. In a telephone system, telephone lines, an automatic switch, a holding trunk, means for making some of said lines busy, a calling deviceon a calling one of said lines for operating said switch to extend a connection to a busy or idle one of said lines` .lneans operative upon the response of a subscriber f for connecting` the line called with said hold- 'ing trunk, release mea-ns in said switch operative in case a busy line is encountered for releasing said switch and for connecting said tone to said calling line, and means operative responsive to the rst subsequent 0peration of said callingvdevice to disconnect said ton-e.

6. In a telephone system, telephonelines, an automatic switch, means for making some of said lines busy, means controlled from a calling oneI of said lines for extendine a connection to a busy or idle one of said lines by operating said automatic switch, said switch operative to extend a talking connection to the called line only in case such line is busy.

7. In a telephone system, telephone lines,

an uitoinaticr switch, a holding trunk associated therewith, means controlled from -a (.alling one ot said lines for extending a connection to a called one of said lines by way ot. said automatic switch, means responsive to the `operation of said switch for disconnecting said holding trunk from saidrswitch, means responsive to the response of the subscriber on the said called. line for associating said line with said holding trunlcand for releasing said. automatic switch, and means responsive to such release for again associating said holding trunk: with said switch.

8. In a telephone system, subscribers lines, a `conference trunk, an lautomatic switch for extending connections to any one of said lines either busy or idle, means in said switch operative if the line is busy for informing the calling subscriber of the busy condition of the line called and for permitting the calling subscriber to converse with the called subscriber regardless of this fact, means in said switch for causing the called subscribers line signal to be operated automatically if the called line is Iidle, and means automatically responsive to the removal of the receiver at the station of the called line for connecting said line to the conference trunln and for effecting the release of said automatic switch.

9. In a telephone system, subscribers lines, a conference trunk, an automatic switch for connecting a plurality of said lines with said trunk, means in said switch for automatically signalling a called station in case the line called is idle, means automatically operative upon the response of the subscriber called for effecting the connection of the called line withthe conference trunk and for effecting the release of said switch, and means operative in case the line called is busy for establishingl a talking connection therewith without effecting the release of said switch.

l0. In a telephone system, subscribers lines, a conference trunk, an automatic switch for extending connections to any desired ones of said lines, means in said switch for automatically signalling a called station in case the line called is idle, means automatically operative upon the response of the subscriber called for effecting the connection of the called line with the conference trunk and for effecting the release of said switch, means for making said lines busy, and means in said switch permitting the same to extend talking connections to busy lines, said last means also effective to permit said first means to function as soon as the called busy line becomes idle.

l1. In a telephone system, a conference trunk, subscribers lines, a directively controlled automatic switch for extending connections to any one of said lines, means associated with each line for causing the same to be connected to the conference trunk when the subscriber called responds, means effective upon such response for effecting the release of said automatic switch to render the same operative to extend a connection to a second called line, and circuit arrangements such that said switch may be operated and 'automatically released repeatedly to cause other of said lines to be connected to said conference trunk.

12. In a telephone system, subscribers lines, a conference trunk, an automatic switch for connecting with and for then transmitting signalling current to said lines, means controlled by the response of subscribers called via said switch for establishing a direct talking connection between the JOHN E. GARDNER. 

